The present invention relates to an electrophotosensitive material suitably used in an image forming apparatus such as an electrophotographic copying apparatus.
Recent years, it is a common practice to use, as the electrophotosensitive material used in an image forming apparatus such as an electrophotographic copying apparatus, an organic photosensitive material economically manufactured because of good workability and having a great degree of freedom of function designing. Particularly, there is proposed an electrophotosensitive material of the function separated type having a photosensitive layer containing a charge-generating material for generating an electric charge by light irradiation and a charge-transferring material for transferring the generated electric charge.
In the electrophotosensitive material of the function separated type above-mentioned, the characteristics of the charge-generating material and the charge-transferring material exert a great influence upon the electric and photosensitive characteristics of the resultant electrophotosensitive material. Accordingly, studies have been made on a variety of substances. As the charge-transferring material, there are proposed a variety of substances such as polyvinylcarbozol, oxadiazol compounds, pyrazoline compounds, hydrazone compounds and the like.
In the charge-transferring materials above-mentioned, however, the drift mobility representing the charge transferring ability is relatively small. Further, since the dependency of the drift mobility upon the electric field intensity is great, the movement of the charge in a low electric field is small. This makes it difficult that the residual potential disappears. Further, such materials are disadvantageously apt to be deteriorated due to irradiation of ultraviolet rays or the like.
On the other hand, it is known that the charge-transferring material of the triphenylamine type presents a small dependency of the drift mobility upon the electric field intensity. For example, the U.S. Pat. No. 3,265,496 discloses, as examples of such a material, N,N,N',N'-tetraphenylbenzidine, N,N,N',N'-tetraphenyl-1,4-phenylenediamine, N,N,N',N'-tetraphenyl-1,3-phenylenediamine and the like. These charge-transferring materials have good molecular symmetry so that the interaction among the molecules is great and the interaction with the resin is small. This presents the problem that these materials are apt to be crystallized in the resin. Thus, these charge-transferring materials cannot be practically used.
In view of the problems above-mentioned, the inventors of the present invention have proposed as a compound presenting a small dependency of the drift mobility upon the electric field intensity and a good compatibility with the resin, a m-phenylenediamine compound which may contain any number of substituents as far as such substituents may be introduced to the respective phenyl rings of N,N,N', N'-tetraphenyl-1,3-phenylenediamine (Japanese Patent Application No. 301703/1987).
Further the inventors of the present invention have found that, when the m-phenylenediamine compound is applied to the electrophotosensitive material, the characteristics of the electrophotosensitive material depend on the positions of the substituents contained in the phenyl rings of the m-phenylenediamine compound.
More specifically, the inventors of the present invention have found that the compound containing substituents introduced to the para-positions of the phenyl rings of the N,N,N',N'-tetraphenyl-1,3-phenylenediamine with respect to the position wherein nitrogen atoms are bonded, presents a high carrier injection efficiency and a great carrier mobility (Japanese Patent Application No.187311/1988). The inventors of the present invention have also found that the compound containing substituents introduced to the meta-position of the respective phenyl rings of the N,N,N',N'-tetra-phenyl-1,3-phenylenediamine with respect to the position wherein nitrogen atoms are bonded, presents a small symmetry of molecules so that the interaction of the molecules is small, and also presents a great interaction with the resin so that the compound is hard to be crystallized in the resin (Japanese Patent Application No.187312/1988).
When the compound above-mentioned containing the substituents introduced t the para-positions is applied to the electrophotosensitive material, this electrophotosensitive material presents high sensitivity. However, when this compound is used in a high concentration, it is disadvantageously apt to be crystallized. The compound containing the substituents introduced to the meta-positions is superior in that this compound is hard to be crystallized. However, this compound presents a low yield to decrease the productivity. Accordingly, when this compound is applied to the electrophotosensitive material, the electrophotosensitive material itself is high in cost.